TITLE: The Why of X AUTHOR: Eugene Wallingford DATE: June 26, 2009 4:01 PM DESC: ----- BODY: Where did the title of my previous entry come from? Two more quick hits tell a story. Factoid of the Day On a walk the other night, my daughter asked why we called variables x. She is reviewing some math this summer in preparation to study algebra this fall. All I could say was, "I don't know." Before I had a chance to look into the reason, one explanation fell into my lap. I was reading an article called The Shakespeare of Iran, which I ran across in a tweet somewhere. And there was an answer: the great Omar Khayyam.

Omar was the first Persian mathematician to call the unknown factor of an equation (i.e., the x) shiy (meaning thing or something in Arabic). This word was transliterated to Spanish during the Middle Ages as xay, and, from there, it became popular among European mathematicians to call the unknown factor either xay, or more usually by its abbreviated form, x, which is the reason that unknown factors are usually represented by an x.

However, I can't confirm that Khayyam was first. Both Wikipedia and another source also report the Arabic language connection, and the latter mentions Khayyam, but not specifically as the source. That author also notes that "xenos" is the Greek word for "unknown" and so could be the root. However, I also haven't found a reference for this use of x that predates Khayyam, either. So may be. My daughter and I ended up with as much of a history lesson as a mathematical terminology lesson. I like that. Quote of the Day Yesterday afternoon, the same daughter was listening in on a conversation between me and a colleague about doing math and science, teaching math and science, and how poorly we do it. After we mentioned K-12 education and how students learn to think of science and math as "hard" and "for the brains", she joined the conversation with:

Don't ask teachers, 'Why?' They don't know, and they act like it's not important.

I was floored. She is right, of course. Even our elementary school children notice this phenomenon, drawing on their own experiences with teachers who diminish or dismiss the very questions we want our children to ask. Why? is the question that makes science and math what they are. Maybe the teacher knows the answer and doesn't want to take the time to answer it. Maybe she knows the answer but doesn't know how to answer it in a way that a 4th- or 6th- or 8th-grader can understand. Maybe he really doesn't know the answer -- a condition I fear happens all too often. No matter; the damage is done when the the teacher doesn't answer, and the child figures the teacher doesn't know. Science and math are so hard that the teacher doesn't get it either! Better move on to something else. Sigh. This problem doesn't occur only in elementary school or high school. How often do college professors send the same signal? And how often do college professors not know why? Sometimes, truth hits me in the face when I least expect it. My daughters keep on teaching me. -----